The invention relates to zoom lenses suitable for image pickup devices that are used in ultra-compact digital cameras, ultra-compact digital video cameras, portable telephones, personal digital assistants (PDAs), and the like.
Imaging optical apparatuses, such as digital cameras or digital camcorders that use image pickup devices, such as charge coupled devices (CCDs) or complementary metal-oxide semiconductors (CMOSs), are currently used widely. Accordingly, zoom lenses that have high performance and are compact and lightweight are required.
As for recent interchangeable lens cameras allowing users to interchange lenses with lenses suitable for a desired viewing angle and desired brightness according to their photographing purposes, demand for cameras having high optical performance and a portable compact size has increased.
In wide-angle zoom lenses having a viewing angle of 70° or greater and a magnification of around 2.5×, a 4-group zoom lens having four lens groups, respectively having negative, positive, negative, positive refractive power, is usually used.
Zoom lenses in which a lens group having a negative refractive power is located in the front have a relatively short minimum object distance (MOD) and thus relatively easily perform view angle-widening. In addition, the zoom lenses can relatively increase a back focal length. Thus, the zoom lenses are widely used as wide-angle zoom lenses. Since such a zoom lens has a positive refractive power from first and second lens groups and a negative refractive power from third and fourth lens groups at a telephoto position, the entire optical system of the zoom lens can have a telephoto structure. Therefore, the zoom lens can easily perform long focusing at the telephoto position.
However, it is difficult to provide a design that satisfies optical performance and miniaturization at the same time. For example, a zoom lens designed by using 12 lenses to achieve aberration correction has been proposed. However, the number of lenses used is too large to achieve a compact structure, and the costs for manufacturing the zoom lens are high. A zoom lens optical system having 10 lenses, including a plastic aspherical lens, and providing magnification of 3× has also been proposed. However, since a plastic lens degrades in optical performance due to double refraction and degrades in optical performance according to a change in temperature, humid, or the like, it is difficult to secure high optical performance that is required by high-pixel digital cameras.